<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

</body>
<script>
    var year = prompt('请输入年份')
    if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
        alert('您输入的是闰年')
    } else {
        alert('您输入的是平年')
    }
</script>

</html>